Laboratoire Jean Perrin

Laboratoire Jean Perrin (LJP) gathers a group of scientists with interest in research at the frontiers between Physics and Biology and this is definitely the essential identity of the laboratory.

LJP’s research activities cover a wide range of fields, from physical chemistry to theoretical statistical physics through soft condensed matter, and are thus organized in distinct research "Themes". However, all these themes are united by the fact that they address biological phenomena through physics-based methods.

In some themes, LJP’s researchers directly work with entire living model biological systems as in the cases of the research performed on the neurobiology of zebrafish and on the physics and quantitative biology of bacterial systems. In other themes, synthetic bio-inspired models are elaborated and investigated to address different biological questions.

This is the case in the studies dedicated to the properties of membrane systems and the morphology of mitochondria, in the research performed on contact mechanics within the framework of tactile perception and tissue mechanics and in the research designing molecular reactive systems to explore morphogenesis laws linked to reaction-diffusion processes.

The situation is somewhat different concerning the theoretical activities with an even broader range of questions from the scale of single molecules to the scale of populations but again with the common denominator of drawing inspiration from biological systems.

Research activities of LJP are organized along 7 themes :

  • Zebrafish behavior and calcium imagery : The rapid progress of modern neurosciences strongly relies on technological breakthroughs, both for stimulation, where a large effort is driven towards the production of complex (natural-like) sensory environments, and for neural recordings, where the main challenge is to obtain long-term measurements of the activity of a significant fraction of the neurons with single-cell resolution on intact animals. We aim at developing experimental tools to address both issues on a specific animal model, namely zebrafish larvae.
  • Micro-organisms biophysics : Microorganisms represent the dominant forms of life on Earth. They display a huge diversity of geometric shapes, behaviours and habitats. We are particularly interested in bacteria. Their size — on the order of microns — and their lifetime — on the order of hours — enable exploring from single cell level to heterogeneous, socially organized populations. We study these systems based on the development of dedicated microfabricated microfluidic devices, coupled with the most recent advances in genetics and video-microscopy and fluorescence imaging approaches. Our objective is to understand the mechanisms underpinning the behaviour of these systems under controlled environments, unveiling the causal relationships linking their physical and biological properties.
  • Biomimetic approach of tactile perception and Contact mechanics :  Our research program focuses on the processes of mechanotransduction along 3 complementary axes, from the macroscopic length scale down to the molecular and cellular length scales, using biomimetic approaches and a simple biological system. At the macroscopic length scale, we study the in-mouth perception of complex fluids. At the molecular/cellular length scales, we are designing model mechanoreceptors stimulated in controlled mechanical conditions. We are also exploring the mechanotransduction processes involved in a unicellular eukaryote microorganism, the paramecium. More recently we started studying the mechanics of tissues in biomimetic systems.
  • Morphogenesis in molecular systems : We take inspiration from early embryo development to engineer synthetic biochemical systems that are capable of spatio-temporal self-organization. The objective of our biomimetic approach is two-fold. On the one hand, by studying simple, physics-like and controllable molecular systems that retain the essential features of their biological analogues we hope to provide new insights on the emergence of complex biological behaviors -such as gene regulation, and morphogenesis. On the other hand, these dynamic molecular systems can be regarded as a new kind of "life-like" materials capable of adapting and responding autonomously to their environment. To this end we essentially use systems based on nucleic acid hybridization reactions because their reactivity can be easily predicted by, roughly, Watson-Crick pairing rules. These systems self-organize in space and time through two archetypal mechanisms: reaction-diffusion and active matter. 
  • Biomembrane plasticity and cellular function : We are particularly interested in mitochondrial membranes. In eukaryote cells, mitochondria are key organelles for energy production and apoptosis that constantly fuse and divide. Two membranes constitute their envelope, with different levels of permeability. A hallmark of the inner mitochondrial membranes (IMM) is the presence of dynamic invaginations called “cristae”. These nanostructures (20-50 nm), rich in a specific mitochondrial phospholipid, the cardiolipin (CL), can change their shape and their density depending on energy demand. Their relative integrity is usually considered as a relevant indicator of the functional state of mitochondria, since cristae contain the OXPHOS complexes responsible for ATP production and they sequester Cytochrome C which release is involved in apoptotic signaling. Specific alterations of cristae morphology induce mitochondrion dysfunctions (in the Barth syndrome for example), and in many pathological situations, such alterations are also observed. Thus, our goal is to understand the role, the dynamic and the impact of cristae on mitochondrial function.
  • Stochastic dynamics of reactive and living systems :  The team is made of theoretical physicists, who study non-equilibrium properties of stochastic systems and their application to the modeling of living systems. Our work combines modeling of experimental systems from the scale of single molecules to the scale of populations, and development of analytical and numerical tools. The group is in constant interaction with various experimental groups.
  • Mesoscopic modelling of biopolymers : Our objective is to develop a tool of modelling and simulation of nucleic acids (NA). The proposed approach consists in describing the conformation as a flexible beam, represented by a ribbon, by means of the theory of non-linear elasticity of beams.